1. Field of the Invention
This invention relates to clamping devices and more particularly to a hand clamp of novel construction having improved operating characteristics.
2. Description of the Prior Art
Among the widely used clamps on the market at the present time is the so-called "C" clamp. This clamp usually has a relatively slow operating speed because a single screw is employed to open and close the jaws of the clamp with the result that a compromise must be made in selecting the pitch of the screw thread to provide both the required mechanical clamping force and operating speed. The "C" clamp also has a tendency to twist the work when flat, hard pieces are clamped together and requires a substantial operating force to tighten the clamp because of the frictional engagement of the end of the screw with the socket of the movable jaw which is pivotally mounted on the screw. This clamp may also be unsuitable for use in many applications where space is limited because of its relatively large length. For example, regulations adopted under the Federal "Occupational Safety and Health Act" mandate the use of plastic or cage type safety guards in certain types of industrial operations. The physical size of the required guard will therefore often be a limiting factor when deciding the type of clamp to be used in a particular operation.
The toolmakers parallel clamp, which has a pair of flat parallel jaws operated by two parallel screws, eliminates many of the problems of the "C" clamp, such as twisting of the work, for example. However, this type of clamp is suitable for use only with flat, hard work pieces because of the necessity of keeping the jaws in a parallel relationship to secure a satisfactory clamping action. Another type of clamp which eliminates twisting of the work has first and second bent arms having jaws pivotally mounted at one end thereof. The other end of the first arm is pivotally mounted on the second arm at a point intermediate the ends thereof and the other end of the second arm is pivotally connected to the apex or elbow which is intermediate the ends of the first arm by means of a single screw, so that twisting of the work is eliminated. However, the socket mounting of the end of the single screw produces frictional loss and the mechanical configuration of the arms produces an operating speed for the jaws which is relatively slow when the jaws are wide open and which gets progressively faster as the jaws are closed, which is the reverse of the operating speed characteristic usually desired.